As a material of a high frequency induction coil serving as a medium for supplying energy to plasma, silver or copper which has low electric resistivity is used. However, the electric resistivity is not zero. Consequently, heat of approximately 10 W to 100 W is generated in the high frequency induction coil. A calorific value depends on a high frequency power value or a surface state (oxidized state or the like) of the high frequency induction coil. As a method of preventing the resistivity of the high frequency induction coil from being changed or impaired due to the heat generation, a cooling method of circulating water (JP-UM-A-H05-50649) is known. That is, the high frequency induction coil has a structure in which a pipe is wound around a plasma torch so that cooling water flows into the pipe. Here, the cooling water is subjected to circulation and heat exchange by using a cooling water circulating device belonging to an inductively coupled plasma device. In addition, a method is also known which cools the induction coil by blowing air from the outside, circulating gas in the pipe, or using a heat pipe (JP-A-H08-203692).
As illustrated in FIG. 7A, JP-UM-A-H05-50649 discloses an inductively coupled plasma mass spectrometer which can miniaturize a drive mechanism for moving a high frequency induction coil 100, and in which cooling water is caused to circulate in the high frequency induction coil 100 via a flexible pipe 101 and a pipeline 102.
As illustrated in FIG. 7B, JP-A-H08-203692 discloses an inductively coupled plasma generating device which can prevent a temperature increase of an output coil (high frequency induction coil) 200, since the output coil 200 is configured to include a heat pipe, a high frequency application terminal 201 functions as an evaporator, a ground terminal 202 functions as a condenser, a heat sink 204 is cooled by a fan 203, and heat generated by the output coil 200 is efficiently transferred to the heat sink 204 through the output coil 200 so as to be discharged to the air.
When the cooling water disclosed in JP-UM-A-H05-50649 is used, the following problems arise. The cooling water circulating device has heat exchanging efficiency of approximately 50%, and a pump for circulating the cooling water consumes energy. That is, the cooling water is cooled by consuming energy more than heat energy generated in the high frequency induction coil, thereby causing environmental burdens. Since the cooling water circulating device is additionally installed, the cost increases. In addition, when the cooling water is used, maintenance work for a cooling water system is needed in order to avoid accidents resulting from water leaks or clogged pipelines. Consequently, the maintenance work inevitably requires labor and cost.
In addition, when the high frequency induction coil is cooled by gas instead of the water, cooling capacity is inferior to that in water cooling. Thus, the high frequency induction coil is operated in a state where the temperature is higher than that in the water cooling. For this reason, a surface of the high frequency induction coil is progressively oxidized. Then, electric resistance of the high frequency induction coil varies with the lapse of time, and the power of plasma varies with the lapse of time, even if a high frequency output of the inductively coupled plasma generating device remains unchanged. That is, even when analysis conditions of the inductively coupled plasma analysis device are not changed, there is a problem in that the power of the plasma varies with the lapse of time and the analysis capability also varies.
The high frequency induction coil itself disclosed in JP-A-H08-203692 is the heat pipe. However, JP-A-H08-203692 does not disclose a specific configuration of the heat pipe except that the heat pipe is disposed horizontally, and does not consider liquid circulating efficiency. In addition, an evaporator of the heat pipe is disposed in an output coil terminal rather than a coil section which becomes hottest in the high frequency induction coil. Consequently, there is a problem in that cooling efficiency becomes poor without utilizing characteristics of the heat pipe. Then, in order to radiate the heat generated in a high frequency induction coil, it is indispensable to install a cooling fan for cooling a condenser. The cooling fan is operated to radiate the heat, thereby causing environmental burdens. Therefore, there is a problem in that the cooling fan results in an increased cost of the inductively coupled plasma analysis device.